1. Field of the Invention
The invention relates to an improved method of producing 3,5,5-trimethylcyclohex-2-ene-1,4-dione (KIP) by the oxidation of 3,5,5-trimethylcyclohex-3-ene-1-one(.beta.-IP) in the presence of mangansalene-like catalysts and certain catalytic additives. ##STR2##
2. Background Information
KIP is an important intermediary product in the synthesis of trimethylhydroquinone, an initial substance in the synthesis of vitamin E. Furthermore, KIP is an initial compound for the synthesis of various carotinoids. ##STR3## State of the art
It is known that .beta.-IP can be oxidized to KIP by molecular oxygen in the presence of a transition-metal-containing catalyst (DE-OS 24 57 157, DE-OS 38 42 547). The use of mangansalene is described in DE-OS 26 19 254.
The space-time yield (product in kg per hour and reaction volume in liters) as well as the amount of catalyst necessary for this are of decisive importance to the economy of a catalytic process. Of the above-mentioned methods for the synthesis of ketoisophorone, the reaction of .beta.-IP with O.sub.2 in the presence of mangansalene complexes of the composition shown above has the best selectivities and space-time yields.
DE-OS 26 10 254 reports in example 11 about a selectivity of homogeneous catalytic oxidation of 100%. A space-time yield (RZA) of 0.09 kg/(hr.multidot.1) can be calculated from the data contained in it. Even these not very convincing values were no longer mentioned in a scientific publication by the same authors (M. Constantini, A. Dromard, M. Jouffret, B. Brossard, J. Varagnat, J. Mol. Catal 1980, 7, 89-97) a few years after the public disclosure of the application. A maximal KIP selectivity of only 85% is disclosed therein, which is achieved with mangansalene as oxidation catalyst. The influence of the educt concentration on the selectivity had not been investigated previously. The problems which can occur upon an increased educt concentration (here &gt;90%) (selectivity 55%, RZA: 0.08 kg/hr.multidot.1 (20.degree.-23.degree. C., O.sub.2 =1 bar)) can be read only from example 17 of DE-OS 26 10 254.
A disadvantage in these methods is the large amount of solvent which must be used in order to assure a high selectivity.
JP-OS 64-90150 teaches a similar method in which, however, the Mn is used in oxidation stage III in the mangansalene.
JP-OS 1-175955 possibly aims in the same direction since, according to the method it describes, the manganese complex is oxidized with tert. alkylhydroperoxides before its usage as catalyst.